Method of electric resistance seam welding bimetallic element



Patented Sept. 6, 1949 UNlTED' STAT METHOD OF ELECTRIC RESISTANCE SEAM WELDING BIMETALLIC ELEMENT George W. Crise, Columbus, Ohio Application December 7, 1944, Serial No. 567,089

2 Claims. (Cl. 219-40) The object of my invention is to provide an improved and efficient method of making bimetal from pre-drawn strips through the agency of electric welding. g

In the present art of producing bimetal of the type employed in thermostatic controls, it is customary to start production by welding together two large ingots of dissimilar metals, such as Invar and brass, and then by the tedious process of rolling, trimming of edges and annealing, repeatedly performed until the desired thickness is reached, the bimetallic strips are produced. Sheets of bimetal so produced are then cut to form strips of desired width and length, and the finished strips are then inspected for thick and thin spots for determining irregularities in the relative thickness of the two metals that remain on either side of the weld.

In addition to the expensive work of preparing the Original ingots, which includes machining the same all over, cleaning and heat soaking, there are inherent waste from not only the edges which must be trimmed for straightness, but also from imperfections in the weld which develop from continued rolling and spoil large sections of the completed sheets due to unwelded spots in the finished sheet.

Another serious handicap is the fact that the dissimiliar metals have different flow characteristics, causing, quite often, one side to be thinner than the other in spots, which greatly affects the operating characteristics of the finished bimetal.

In my process, I seek to eliminate all the foregoing defects and, in addition, produce a bimetal having greater flexing efllciency and stability over a wide temperature range by eliminating the side stresses which develop in bimetal by wide and medium widths.

It is well known in the field of bimetal manufacture that when the high flex side of bimetal expands with heat, it expands laterally as well as longitudinally. This tends to cause the strip to assume a transversely curved shape, similar to that of a self-straightening steel tape. This transverse stiffening action opposes the longitudinal bending action and introduces stresses in the bimetal which at high temperatures causes the same to assume a set or new shape which destroys the accuracy and sensitivity of the thermostatic equipment of which the bimetal forms an active part.

In the present invention, this effect is eliminated by joining the dissimilar metals of the bimetal only in the central longitudinal region of the strip, leaving the regions on opposite sides of the weld free to slip one upon the other, thereby eliminating lateral strains which produce transverse curling of the strips when the same are formed in accordance with prior practice.

For a further understanding of the nature of the invention, and additional objects and advantages thereof, reference is to be had to the following description and the accompanying drawing, wherein:

Fig. 1 is a side elevational view of the stripforming and welding rolls utilized in my improved process;

Fig. 2 is a sectional view on the line 2-2 of Fig. 1;

Fig. 3 is a similar view on the line Fig. 1.

Referring more particularl to the drawings, the numerals I0 and I l designate two reels which carry strips of dissimilar, cold-drawn or rolled metals, such as brass or Invar. As these strips unwind from the reels, as at l2, they are caused to pass through shaping or forming rolls, indicated at l3, l4 and l5, IS. The rolls l3 and I6 are formed with convex rims, while the rolls M and 15 have concaved rims, as illustrated in Fig. 2. The action of these rolls is to impart a set transverse configuration to the strips so that the side regions thereof are separated, as shown in Fig. 3.

After being so drawn between a pair of copper welding rolls l1 and I8, the latter being energized by the lowvoltage transformer 19, in accordance with the general practice for seam welding. From the rolls I1 and t8, the welded strips, which are joined centrally and longitudinally, as disclosed in Fig. 3, are advanced for passage between a pair of smooth, flat-faced straightening rolls 2i and 2|, where the separated regions or edges are pressed together into smooth, fiat and adjoining relationship to form the complete bimetallic strip, the finished strip being wound on the receiving reel, indicated at 22.

It will be obvious that by using smooth, round edged cold-drawn shapes which are ordinarily referred to in the art as cold-drawn, round edged flat wire, such shapes when welded together in the central longitudinal regions thereof only, and pressed flat, provide a bimetal with smooth, outer longitudinal edges, this being in contrast with the cut strips as are now used, which produce sharp edges and are dangerous to handle. Moreover, the outer edge regions of my improved bimetal another laterally,

strip are free to slip over one '4 while at the same time providing complete and 2. The method of producing bimetallic elements adequate longitudinal unction. strips so formed which comprises forming a pair of strips comthe prevailing practice. I V 1 j engagement and the edge portions thereof sep- Also, in my process; the metals utilized may 10 arated, and uni g said strips by electric resistpossess any suitable relative thickness and can be ance welding the same continuously only along readily joined, thus producing maximum flexure their fiat central portions.

of the finished strip by matching the material 7 g GEORGE W. CRISE. thicknesses according to their modulus of elasticity. 15 REFERENCES CITED I clam The following references are of record in the 1. The method of producing bimetal elements m f this patent; which comprises forming a'pair of transversely W flat strips composed of dissimilar metals into UNITED STATES PA'I'ENTS strips having longitudinally extending flat central 20 Nu ber Na e Date portions and lateral edge tions disposed n 1,220,774 Murray Mar; 7, 1917 angular relation to the central port ons f the 1,991,495 Derby Feb. 19,1935 strips, bringinesaid trips in o, ongi udinal an 1,991,496 Derby Feb. .19, 19 5 vfirtiwlly ali ned j nta e ition w th the entra ions of e hoi he rim abut n rela ion 2 FORE-9N mums and the ge Portions h teof n separ t d relambe Countr a tion, and electric t 21 ,596 Great Britain n 29, 1925 ogether contmu 33,946 Denmark Nov. 29, 1924 s 

